In transmission of data over a cell switched digital communication network, such as an asynchronous transfer mode or ATM network, problems arise when multiple sources send data cells at widely varying rates through a switch node or link of the network at an aggregated rate which taxes the ability of that switch node or link to handle the data. Congestion occurs at the node of a network when data arrives at the node at a rate exceeding the rate at which the node can process and forward the data to other nodes. The excess data then accumulates in buffer storage at the node, which fills at a rate which is the difference between the arrival rate and the processing and forwarding rate. If the congestion persists for long periods of time, the buffer storage will be filled to maximum capacity and any additional data must be discarded.
In an effort to minimize such data loss, an available bit rate or ABR flow control scheme has been developed to prevent or inhibit excess data from entering the network. With ABR flow control, the rate at which the data is permitted to enter the network is controlled to not exceed an allowable cell rate, or ACR, and this ACR is adjusted via a feedback signal, usually in a form of resource management, or RM, cells from a network reflecting the congestion of the network. One such ABR flow control scheme is described in an ATM Forum document af-tm-0056.000 entitled "Traffic Management Specification Version 4.0" authored by the ATM Forum Technical Committee, April 1996.
However, the ABR flow control scheme described in the above ATM Forum document describes mostly the source and destination system behaviors and leaves the switch system behavior unspecified. Although several example switch mechanisms have existed in the past, these mechanisms are either known to not work well, e.g., with fairness and stability problems, or are complicated to implement in switches, e.g., requiring accurate estimation of the ABR traffic load and fair sharing of bandwidth for each ABR connection. Furthermore, none of the switch mechanisms have analytical proof for stability and performance. Most of them were only shown to work by simulations in very small scale networks under very limited traffic conditions. In order to have a complete ABR flow control scheme for vendors to implement in existing ATM networks, it is thus very important to develop an ATM Forum compliant ABR flow control mechanism which is both easy to implement and effective in achieving the objective of ABR flow control, namely making efficient use of network resources.